The basic refractories of the present invention are suitable for use in lining high wear areas of the basic oxygen steelmaking furnaces (BOF). The current practice for lining a BOF requires the use of premium products in the high wear areas to attain a balanced life of all refractories in the furnace. Presently, the premium grade refractories are made from dead-burned magnesite which has been crushed, sized, rebonded by pressing and fired to high temperatures. Penetration by basic slags and metal leading to rapid corrosion of the refractories is reduced by impregnating the refractory shapes with tar or other coal products which will coke when heated. The coking process fills open pores and forms a layer which repels attack by the furnace slags.
Although the tar-impregnated magnesite (in the art and herein used synonymously with magnesia, both terms commonly describing bodies with periclase as the stable crystalline form) have become widely used, there is a continuing interest in decreasing the cost of refractory material consumed per furnace heat or per ton of steel produced. Lower refractory cost per ton of steel can be obtained by replacing current refractories with a cheaper refractory of equivalent life or by replacing with a refractory having superior properties and life which will more than compensate for any greater initial cost.
Of course, a refractory with superior properties and lower cost is always an ultimate goal. With this in mind, experimenters have moved in the direction of dolomite as a replacement or a partial replacement for the MgO in magnesite brick. This replacement accomplishes a cost reduction, because not only is dolomite more readily available commercially, but the energy requirements for one common method of producing high purity magnesite (from magnesium hydrate produced by a treatment of sea water or other brine) are extremely high. In moving toward dolomite as a refractory raw material, we are moving toward the consumption of less energy in both producing the raw material and in burning the refractory.
The use of dolomite, dead-burned dolomite (a mixture of periclase and calcia) or fused dolomite (a resolidified melt of dolomite or equivalent calcia and magnesia) with or without excess magnesia is not without its problems. Perhaps the chief problem involves hydration of the dolomite or dead-burned dolomite grains to form calcium hydroxide with an incident volume expansion and weakening of the body. Fused dolomitic grains have been afforded more attention because of their increased hydration resistance, but they still suffer somewhat from hydration. Accounts of fused dolomitic refractory and grain can be found in U.S. Pat. Nos. 3,540,899 and 3,262,795. Both suggest improvements relating to the art of fusion casting basic refractories.
Finally, the steel production measures of a good refractory (number of heats or tons of steel per brick life) are generally not reproducible in the laboratory for evaluation of samples. Therefore, the properties of corrosion/erosion resistance to synthetic basic slags and hot strength (modulus of rupture, usually at 1340.degree.C unless specified otherwise) provide the quantitative means of comparing laboratory samples. Experience in the art has determined that reliance on these two tests as initial indications of potential furnace life is well founded.